Diving helmet
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Diving helmets are worn mainly by professional divers engaged in surface supplied diving, though many models can be adapted for use with scuba equipment.
The helmet seals the whole of the diver's face from the water, allows the diver to see, provides the diver with breathing gas, protects the diver's head when doing heavy or dangerous work, and usually provides voice communications with the surface (and possibly other divers). If a helmeted diver becomes unconscious but is still breathing, the helmet will remain in place and continue to deliver breathing gas until the diver can be rescued. In contrast, the scuba regulators typically used by recreational divers must be held in the mouth, and will usually fall out of an unconscious diver's mouth resulting in drowning.
Before the invention of the demand regulator, all diving helmets used a free-flow design. Gas was delivered at a constant rate, regardless of the diver's breathing, and flowed out through an exhaust valve. Most modern helmets incorporate a demand valve, which is essentially a scuba regulator. This means that the helmet only delivers breathing gas when the diver inhales. Free-flow helmets use much larger quantities of gas than demand helmets, which can cause logistical difficulties and is very expensive when special breathing mixtures, such as heliox, are used. They also produce a constant noise inside the helmet, which can cause communication difficulties. Free-flow helmets are still preferred for hazardous materials diving, because their positive-pressure nature can prevent the ingress of hazardous material in case the integrity of the suit or helmet is compromised.
Most modern helmet designs are sealed at the neck using a neoprene "neck dam." When the neck dam is integrated with a drysuit, the entire body is isolated from the surrounding environment, giving an additional degree of warmth and protection. In hazardous environments such as sewage or dangerous chemicals, a helmet (usually of the free-flow type) is sealed to a special drysuit (usually made of thick rubber) to completely cover and protect the diver. This equipment is the modern equivalent of the historic Mark V "Standard Diving Dress", and is commonly referred to as "heavy gear."
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[edit] Types
Historically, deep sea diving helmets ranged from the two bolt to four bolt helmets; helmets with six, eight, or 12 bolts; and Two-Three, Twelve-Four, and Twelve-Six bolt helmets.
Notable modern commercial helmets include the Kirby Morgan Superlite-17B from 1975 and developments from that model. These helmets are of the demand type, built on a fiberglass shell with chrome-plated brass fittings, and are considered the standard in modern commercial diving for most operations. [2]
The Desco "air hat" is a metal free-flow helmet, designed in 1968 and still in production. Although it has been updated several times, the basic design has remained constant and all upgrades can be retrofitted to older helmets. Its robust and simple design (all maintenance can be performed in the field with only a screwdriver) makes it popular for shallow-water operations and hazardous materials diving. The Desco is secured to the diver by means of a "jock strap" which runs between the legs, and its buoyancy can be fine-tuned by adjusting intake and exhaust valves.
Light-weight transparent dome type helmets have also been used. For example the Sea Trek surface supplied system, developed in 1998 by Sub Sea Systems, is used for recreational diving.[3]. Also the Lama, developed by Yves Le Masson in the 1970s, has been used in television to let viewers see the face and hear the voice of the presenter speaking underwater. [4]
[edit] History
See Diving helmets appear for the history of the diving helmet.
Augustus Siebe is known as the father of Diving. In the year 1837 German-born inventor Augustus Siebe, then living in England, developed a Diving Helmet which was sealed to a watertight, air-containing rubber suit. The closed diving suit, connected to an air pump on the surface, becomes the first effective standard diving dress, and the prototype of hard-hat rigs still in use today. In his obituary Siebe is described as the father of diving.
Siebe Gorman & Co was notable for developing the “closed” diving helmet of the standard diving dress and associated equipment. As the helmet was sealed to the diving suit, it was watertight, unlike the previous “open” helmet systems. The new equipment was safer and more efficient and revolutionised underwater work from the 1830s.
However, Alexander McKee proposed that brothers John and Charles Deane were the true inventors, and that Siebe was the leading manufacturer of their designs.[5]
[edit] Nowadays
An alternative to the diving helmet that allows communication with the surface is the full face diving mask. These cover the diver's face and are held onto his head by adjustable straps.
"Diving helmet" sometimes means a hard safety helmet like a workman's helmet that covers the top and back of the head, but is not sealed. These may be worn with a full-face mask to provide impact protection.
During the First World War the British Army used a few diving helmets out of water as emergency protection from mustard gas.
[edit] See also
[edit] References
- ^ Curley, MD (1986). "Human Factors Evaluation of the Superlite 37B Helmet in the Surface- Supplied, Open-Circuit Mode". US Navy Experimental Diving Unit Technical Report NEDU-11-85. http://archive.rubicon-foundation.org/3527. Retrieved 2008-09-09.
- ^ Kirby Morgan DSI dive helmets
- ^ Sea Trek dive helmet
- ^ Lama dive helment
- ^ The Infernal Diver by John Bevan, Hardcover - 314 pages (27 May, 1996), Submex Ltd; ISBN 0-9508242-1-6
